1. Field of the Invention
The present invention relates to a process for producing a 1,4,4a, 9a-tetrahydroanthraquinone compound which is useful as an intermediate of organic chemicals especially dyes, by reacting 1,4-naphthoquinone with a conjugated diolefin. More particularly, it relates to a process for producing 1,4,4a,9a-tetrahydroanthraquinone by reacting 1,4-naphthoquinone with a conjugated diolefin in a reaction medium of 1,4,4a,9a-tetrahydroanthraquinone.
2. Description of the Prior Art
In the production of a 1,4,4a,9a-tetrahydroanthraquinone compound (hereinafter referred to as THAQ compound) by the Diels-Alder reaction of 1,4-naphthoquinone (hereinafter referred to as NQ) with a conjugated diolefin, the reaction has been carried out in an inert medium, for example an aromatic hydrocarbon such as benzene, xylene and naphthalene. However, in order to complete the reaction, it is necessary to use more than equimole of a conjugated diolefin to NQ and to recover excess conjugated diolefin after the reaction. In the conventional process using an organic solvent, the conjugated diolefin has high affinity to the solvent and accordingly, the recovery of the conjugated diolefin has not been easy. When THAQ compound is obtained from the reaction mixture, the organic solvent should be separated from the reaction mixture including the organic solvent. A step of separation and recovery of the organic solvent such as distillation is required. Even though it is disilled in vacuum, the organic solvent is not easily separated and a portion thereof is remained. It has been difficult to completely separate the solvent.